Development and Fundamental Understanding of Self-healing Flexible Li-S Batteries with High Cycle Stability (FlexBatt)

成功设计出具有高能量密度的未来锂电池，有望显著改善现有电池技术，并推动环保汽车的发展。Li-S电池的能量密度是现有锂离子电池的三倍，具有快速充放电循环的高可逆性和数千次循环的寿命。锂- s电池的最新进展表明其运行机制复杂，因此需要进一步深入的机理研究和所有电池组件的材料开发。主要的性能和稳定性限制因素与电导率、多硫化物溶解和氧化还原穿梭现象、体积膨胀和电极钝化有关。柔性电池允许采用任何所需的形状。使用自我修复材料，通过自我修复来修复由体积膨胀产生的裂缝，可以在大量循环中保留导电途径。本文提出的概念“flexbattery”包含了整个锂电池的柔性组件的开发。阳极、阴极、分离器和固体聚合物电解质将以一种凭借自修复材料实现灵活性的方式设计。此外，弯曲行为与电池性能之间的关系将通过流变学（流变阻抗）和操作中的电化学和光谱方法进行研究。一种柔性的、独立的、低粘结剂含量的阴极将基于柔性硫-共聚物-碳纳米管网络开发。这些将与新型弹性固体电解质和锂沉积纺织阳极相结合。结合流变学和恒电位器的定制装置将用于了解电极通过蠕变和松弛现象的自愈行为。通过阻抗分析监测变形前、变形后和自愈后的阻抗数据。在电化学循环过程中，离子在膜上的传输和形态变化将通过in-operando技术来研究，以了解循环性能和弯曲行为之间的关系。通过小角度x射线散射、显微镜和光谱学方法对电极进行间歇性分析，以确保其自愈特性。在多次充放电循环和不同放电深度后，将对电池部件进行事后分析，以了解电池在不同弯曲角度下的功能和耐久性。完整的研究旨在了解整个柔性电池的机械化学稳定性的重要性，并最终将深入了解硫/有机硫物种限制电池性能和寿命的不可逆反应的机制和命运。

The design of successful future Li-S batteries with high energy density has the prospect to significantly improve existing battery technology and boost environmentally friendly automotive development. Li-S batteries could triple the energy density relative to existing Li-ion batteries combined with high reversibility of fast charging-discharging cycles and lifetime of thousands of cycles. Recent progress on Li-S batteries indicates a complex mechanism of operation, and hence calls for further in-depth mechanistic studies and material development of all battery components alike. Major performance- and stability-limiting factors are related to conductivity, polysulfide dissolution and redox shuttle phenomena, volume expansion and electrode passivation by (poly)sulfides. Flexible batteries allow to adopt any desired shape. The use of self-healing materials that undergo autonomous self-repairing to heal cracks created by volume expansion could retain conductive pathways for a high number of cycles. The herein proposed concept "FlexBatt" encompasses the development of flexible components for an entire Li-S battery. Anode, cathode, separator and solid polymer electroyte will be designed in a way that flexibility is realized by virtue of self-healing materials. Moreover, the correlation between flex behavior and cell performance will be studied by rheology (rheo-impedance) and in-operando electrochemical and spectroscopic approaches. A flexible, free-standing, low binder content cathode will be developed based on flexible sulfur-copolymer-CNT networks. These will be combined with novel elastomeric solid electrolytes and a lithium-deposited textile based anode. A custom-build setup combining rheology and potentiostat will be used to understand the self-healing behavior of the electrodes by creep and relaxation phenomena. Impedance data before appying deformation, after deformation and after self-healing will be monitored by impedance analyses. During electrochemical cycling, ion transport across the membrane and morphological changes will be investigated by in-operando techniques to understand the correation between cycle performance and flex behavior. Intermittent analyses of the electrodes to ensure the self-healing properties will be conducted by small anagle X-ray scattering, microscopy and spectroscopic approaches. The post-mortem analysis of the cell parts after multiple charging-discharging cycles and at different depth of discharge will be carrried out to understand the functionality and durability of the cell operated at different bending angles. The complete study aims at understanding the importance of mechano-chemical stability of the entire flexible battery and finally will provide insight into the mechanism and fate of irreversible reactions of sulfur/organosulfur species limiting battery performance and life time.